This invention relates to a burner and, more particularly, to a burner for gas turbine engines having a ring-shaped swirling device which is coaxially assigned to a fuel nozzle. The swirling device forms tangential ducts between profiled surfaces distributed along the circumference for an adjustable feeding of combustion air.
In the case of modern burners and combustion chamber designs for gas turbine engines, a combustion that is low in pollutants is endeavored, particularly in the primary zone of the combustion chamber. It was found that a significant reduction of the emission of pollutants can be achieved in the case of a comparatively low combustion temperature of &lt;1,900.degree. K by means of a comparatively high proportion of air with respect to the fed fuel in the primary zone.
In addition, relatively low pollutant emissions require, among other things, a uniform processing of the fuel-air mixture to be supplied to the primary zone as well as good combustion efficiency. This is particularly true in the case of burners known according to German Patent Document DE-PS 24 42 895 which operate with air support as "low-pressure systems" with a high fuel atomization efficiency and a partial wall-side and aerodynamic fuel evaporation. However, the known case does not provide swirling devices which can be adjusted with respect to the air flow rate in order to control different operating conditions with respect to correspondingly required variable fuel-air flow rates, in a manner that is as low in pollutants as possible.
Furthermore, combustion chamber concepts which, in the interest of a combustion that is low in pollutants, provide a "variable chamber geometry" in order to supply combustion air and possibly mixed air by way of holes of the rows of holes are high in construction expenditures, technically complex, susceptible to disturbances and expensive. These devices can be controlled in their cross-sections by pipe sections of the flame tube jacket of the combustion chamber which can be displaced relative to one another in the axial or circumferential direction.
From European Patent Document EP-PS 0251895, an annular combustion chamber for a gas turbine engine is known. In this case, for a combustion that is low in pollutants, an "external" swirling device is assigned to each burner which can be regulated with respect to the supply of a portion of the combustion air.
In the known case, the regulating takes place via a screen which can be rotated on the outside on a central body in the circumferential direction and which has webs on openings distributed along the circumference. The webs, according to their length, project only partly into radial/tangential openings of the central body. The webs project in such a manner that, in intermediate positions of the screen, they each have an angular position which deviates from the openings. In the intermediate positions which are decisive for the regulating, a guiding of the duct is obtained which throttles the air flow at the inlet, is divergent in the direction of the flow and expands abruptly downstream of the trailing edge of the web in the direction of a large-surface duct outlet. In the process, the respective circumferential component of the flow at the respective outlet of an opening is clearly weakened in the, manner of a separating diffuser flow, whereby the required generating of the swirl is impaired considerably. This is a significant disadvantage with respect to obtaining a uniform development of turbulence which is required during the whole, operating condition and a resulting uniform and stable combustion that is low in pollutants.
There is therefore needed a burner of the initially mentioned type wherein in a relatively simple manner, at least one swirling device permits over a large control range the air flow rate operationally required for a combustion which is uniform and low in pollutants while a uniformly pronounced rotational swirl is maintained.
According to the present invention, these needs are met by a burner for gas turbine engines having a ring-shaped swirling device which is coaxially assigned to a fuel nozzle. The swirling device forms tangential ducts between profiled surfaces distributed along the circumference for an adjustable feeding of combustion air. The profiled surfaces are formed by corresponding sections of components which are arranged to be axially movable relative to one another. One respective section of a profiled surface is a hollow body in which the corresponding other section engages in a movable manner.
According to the present invention, the sections which form the profiles or profiled surfaces are arranged in an axially projecting manner on mutually opposite faces of two, possibly ring-shaped, or annual-disk-shaped components. Preferably, the profile sections constructed as hollow bodies may be designed to be relatively thin-walled and to be precisely coordinated with the outer profile geometry of the profile sections of the respective other components which can be axially moved into it.
In the case of the present invention, an axial profile lengthening or shortening is virtually obtained during the relative adjustment with the significant advantage that the recesses which are in each case mutually opposite between the profile sections, develop axially enlargeable or reducible cross-sections of the swirling ducts. This occurs in suck a manner that in all positions, along the whole duct length, flow cross-sections exist which are always maintained to be constant. The front wail course of the hollow-body-type, section which projects slightly in intermediate positions or in the maximally opened end position presents no significant aerodynamic "obstacle". In the case of the present invention, swirling ducts are constructed with respectively continuous square or rectangular cross-sections. The possibility exists to construct the profile sections and thus the profiles and swirling ducts to be radially/tangentially curved in the circumferential direction.
The aerodynamic impairments or disadvantages which were mentioned with respect to the known prior art do not occur either on the inflow or on the outflow side. Despite the adjustment in the sense of a change of the air flow rate, a speed profile exists which, on the outlet side, is uniform along the circumference.
Therefore, because of the indicated characteristics, the swirling flow and thus the desired rotational swirl geometry, which is also responsible for an optimal processing of the fuel/air mixture, will not be impaired in the different intermediate positions.
Using the adjustable swirling device, the whole or a significant portion of the primary air which is required for a combustion that is low in pollutants can be supplied. The swirling device can be adjusted for the flow rate of relatively small and relatively large amounts of air.
In an advantageous further development, the present invention permits the combination of at least one controllable or adjustable swirling device with a stationary swirling device which makes available a constant air supply during the whole operating condition. The fuel supply is varied depending on the load condition, in which case an air supply is "superimposed" on the variable operating conditions which, while being adapted to the respective operating conditions, meets the air requirement with respect to a combustion that is low in pollutants. The latter air requirement may be regulated, for example, as a function of an operationally increasing combustion temperature and/or, pressure in the combustion chamber.
The present invention includes the possibility of burning, for example, stoichiometrically, in certain engine conditions, as well as dependent on the design and use spectrum of the engine, i.e. during the igniting and the start of the operation as well as, possibly, during an extreme full load. The invention also provides burning, predominantly in the cruising operation, with a large amount of air and therefore in a manner that is low in pollutants.
The concerned swirling devices may generate in approximately the same direction or in mutually opposite directions rotational or mixed air swirls which rotate with respect to the burner axis or nozzle axis.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.